The present disclosure relates to a propulsion unit for propulsion and maneuvering of a vessel.
There are known propulsion units that include a propeller section which is fixed in a surrounding rotor part, in the periphery of which there are arranged permanent magnets or windings for providing magnetic field. The rotor part constitutes the rotor of an electrical motor and is positioned inside a surrounding stator part, which stator part is provided with magnetic devices or windings for generating magnetic field for causing rotation of the propeller section.
U.S. Pat. No. 5,220,231 discloses such a propulsion unit for a seagoing vessel. The propulsion unit has a centrally supported propeller section and a radially exterior positioned ring which rotates with a small radial distance from the stator part.
Common for present solutions is that these types of propulsion units are arranged to the vessel hull or a steering device by means of one stem. Solutions like these are, among others, known from U.S. Pat. No. 6,837,757, DE 2744913 A1 and U.S. Pat. No. 3,708,251.
There are several disadvantages of using only one stem which extends between an upper part of the propeller nozzle and the hull or a steering device. Among others, this one stem often creates drag, something which will result in turbulent flow at the top of the nozzle. This turbulent flow will result in directional change of flow which is led into the propellers, which results in that the propeller blades being exposed to variation in pressure and velocity of the inflowing water, ultimately resulting in a reduction in efficiency, and increased noise and vibration.
A solution which partly solves this is described in RU2096254 C2. In RU2096254 C2 it is described a vessel propeller arranged in a nozzle. The nozzle is fixed to the vessel hull by means of two separate frame parts by the use of vibration dampening means. The two frame parts are fixed separately to the hull and this solution can thus not be rotated. A similar solution is also described in U.S. Pat. No. 6,837,757 where two stems extend with a V-shape from the propeller nozzle to the hull for increased fastening stability and short stem cord length. This solution can neither be rotated as it is fixed directly to the vessel.
There is an increasing focus on reducing the energy requirement for the use of all propulsion units for propulsion and maneuvering of vessels. There are continuously set restricting demands for emission of environmentally unfriendly gases and the fuel costs are continuously increasing, all of which have led to an increased focus on developing novel solutions, among others, optimization of propeller blades and development of hybrid systems for propulsion of the vessels.
There is thus a need for providing a propulsion unit which provides reduced generation of turbulence, improved efficiency, and reduced noise and vibration compared to prior art.
There is also a need for providing a propulsion unit which has lower weight, without sacrificing sufficient strength.